The present invention generally relates to anti-aliasing line display apparatuses, and more particularly to an anti-aliasing line display apparatus which is used to make a graphic display of a straight line.
Recently, it has become more popular to generate three-dimensional images on a computer. The users tend to demand more realistic or graphic images, and the problem is whether or not the generated images actually appear realistic. On the other hand, there are strong demands to realize real-time processing.
Aliasing is a phenomenon where a contour line of an object or a boundary line of patterns on the object become jagged on the generated image. In other words, the contour line and the boundary line become stepped. The deterioration of the image caused by this aliasing is particularly notable when the contour line or the boundary line of the image is a straight line.
Accordingly, there are demands to realize a process of effectively eliminating the aliasing. That is, there are demands to realize an apparatus which can positively carry out an anti-aliasing process at a high speed.
Even if a computer generates an image having a high quality by carrying out a three-dimensional image processing, the quality of the image which is displayed is determined by the resolution of a display device which displays the generated image. Generally, the display device used for computer graphics must display the image using a group of a finite number of pixels, and the aliasing is inevitably generated. Due to this aliasing, the displayed line appears jagged or the displayed line may be broken at an intermediate point.
The quality of the displayed image greatly deteriorates when the aliasing is generated, and the anti-aliasing process is carried out to eliminate the aliasing. Conventionally, one of three kinds of anti-aliasing techniques is generally employed.
1) Super Sampling Technique PA0 2) Filtering Technique PA0 3) Z Buffer Technique
With respect to the color of one pixel in a frame buffer, a frame buffer having finer pixels than the actual frame buffer is imagined. For example, the finer pixels are obtained by dividing one pixel into nine divisions. According to this technique, the color calculation is made for each of the finer pixels, and an average value of the colors of the plurality of finer pixels corresponding to one pixel in the actual frame buffer is obtained.
With respect to the color of one pixel in the frame buffer, an average value of the colors of a plurality of pixels neighboring this one pixel is obtained. According to this technique, it is possible to prevent the colors of the adjacent pixels from greatly changing, and as a result, the generation of the aliasing is prevented.
This technique is a modification of the filtering technique. In other words, a differentiating filter is used for a Z buffer, and an averaging filter is applied only to the pixels (edges) which are detected as having discontinuity in the depth. According to this technique, when displaying an image having overlapping objects, it is possible to smoothly display the overlapping boundary portions.
However, according to each of the conventional techniques described above, the color to be displayed is determined by carrying out an averaging process. For this reason, the color to be displayed is not accurately calculated, and there was a problem in that it is impossible to display a smooth straight line. As a result, it was impossible to positively prevent the generation of the aliasing, and the displayed image deteriorated.
If the aliasing is not accurately eliminated when displaying a straight line, the jaggedness becomes particularly notable.